Shock absorber

Abstract

This shock absorber has a first damping force characteristic that is exhibited when a piston speed is from a low-speed region to a high-speed region while a relative position of a piston with respect to a cylinder is in a first range during a low frequency, a second damping force characteristic greater than the first damping force characteristic is exhibited when the piston speed is from the low-speed region to the high-speed region while the relative position is in a second range different from the first range during a low frequency, and a difference in damping force characteristic between during the first range and during the second range is smaller than a difference between the first damping force characteristic and the second damping force characteristic during a high frequency. A second passage is provided with a variable orifice mechanism with a changeable orifice area based on relative position.

The invention claimed is: 
     
         1 . A shock absorber comprising:
 a cylinder in which an operation fluid is sealed;   a piston which is provided in a manner of being able to slide inside the cylinder and divides an inside of the cylinder into a rod-side chamber and a bottom-side chamber;   a piston rod in which one end side is coupled to the piston and the other end side extends to an outside of the cylinder;   a first passage through which an operation fluid flows out from one chamber inside the cylinder in response to movement of the piston;   a second passage which is provided in parallel to the first passage; and   a damping force generation mechanism which is provided in the first passage and generates a damping force,   wherein the second passage is provided with:
 a variable orifice mechanism in which an orifice area is able to change depending on a relative position of the piston with respect to the cylinder; and 
 a frequency sensitive mechanism in which a damping force during a low frequency is greater than a damping force during a high frequency regardless of a piston speed, and 
   wherein the shock absorber is configured such that:
 a first damping force characteristic is exhibited when the piston speed is from a low-speed region to a high-speed region while the relative position of the piston with respect to the cylinder is in a first range during the low frequency; 
 a second damping force characteristic greater than the first damping force characteristic is exhibited when the piston speed is from the low-speed region to the high-speed region while the relative position of the piston with respect to the cylinder is in a second range different from the first range during the low frequency; 
 a third damping force characteristic is exhibited when the piston speed is from the low-speed region to the high-speed region while the relative position of the piston with respect to the cylinder is in the first range during the high frequency; 
 a fourth damping force characteristic is exhibited when the piston speed is from the low-speed region to the high-speed region while the relative position of the piston with respect to the cylinder is in the second range during the high frequency; and 
   a difference between the third dampening force characteristic and the fourth dampening force characteristic is smaller than a difference between the first damping force characteristic and the second damping force characteristic during the high frequency.   
     
     
         2 . The shock absorber according to  claim 1 ,
 wherein the relative position of the piston with respect to the cylinder is closer to a side of the rod-side chamber in the first range than in the second range.   
     
     
         3 . The shock absorber according to  claim 1 ,
 wherein the relative position of the piston with respect to the cylinder is closer to a side of the bottom-side chamber in the first range than in the second range.   
     
     
         4 . A shock absorber comprising:
 a cylinder in which an operation fluid is sealed;   a piston which is provided in a manner of being able to slide inside the cylinder and divides an inside of the cylinder into a rod-side chamber and a bottom-side chamber;   a piston rod in which one end side is coupled to the piston and the other end side extends to an outside of the cylinder;   a first passage through which an operation fluid flows out from one chamber inside the cylinder in response to movement of the piston and which is formed in the piston;   a second passage which is provided in parallel to the first passage;   a damping force generation mechanism which has a first valve provided in the first passage and generating a damping force, and a back pressure chamber applying a back pressure to the first valve;   a tightening member in which at least a part of the second passage is formed;   a flexible member which is disposed inside a case member and is able to flex inside the case member;   a chamber inside the case member which is defined and provided by the flexible member;   a hole which is formed on an inner circumferential side of the piston rod;   a pin member which is inserted into the hole and varies a gap with respect to the hole depending on a position in an axial direction; and   a hollow chamber which is formed by the hole and the pin member,   wherein the hollow chamber communicates with:
 a third passage through which an operation fluid in the rod-side chamber is supplied in a state that does not change based on a relative position between the cylinder and the piston; 
 a fourth passage through which an operation fluid is supplied to the back pressure chamber; 
 a fifth passage through which an operation fluid is supplied to the case member; and 
 a sixth passage through which an operation fluid is supplied to the bottom-side chamber via the tightening, and 
   wherein an operation fluid in the rod-side chamber is supplied to the second passage via the first passage formed in the piston.   
     
     
         5 . The shock absorber according to  claim 4 ,
 wherein the second passage branches from the first passage via an orifice formed by a disk abutting the piston.   
     
     
         6 . The shock absorber according to  claim 4 ,
 wherein a diameter of the pin member is adjusted such that the gap is reduced when a movement amount of the piston to a side of the bottom-side chamber has increased.   
     
     
         7 . The shock absorber according to  claim 6 ,
 wherein the diameter of the pin member is adjusted by chamfering.   
     
     
         8 . The shock absorber according to  claim 4 ,
 wherein when the relative position between the cylinder and the piston is the same in an extension stroke and in a contraction stroke, a damping force characteristic of the extension stroke is not an inverted version of a damping force characteristic of the contraction stroke.